The subject matter of this invention relates generally to vacuum circuit interrupters and relates more particularly to relatively small vacuum bottles for vacuum circuit interrupters.
Vacuum circuit interrupters and vacuum bottles are known. Examples of vacuum bottle arrangements can be found in U.S. Pat. No. 4,440,995 entitled "Vacuum Circuit Interrupter With On-Line Vacuum Monitoring Apparatus" issued Apr. 3, 1984 to Lange et al. and U.S. Pat. No. 3,594,525 entitled "Common Parallel Operating Means for Series-Connected, Laterally Offset Vacuum Switches" issued July 20, 1971 to R. H. Miller et al. Examples of vacuum interrupters can also be found in a brochure entitled "Westinghouse Vacuum Interrupters" B-671. Typically, vacuum circuit interrupters interrupt an electrical arc within a vacuum. Once the circuit is interrupted the distance between the open contacts necessary to withstand the voltage of the circuit thereacross can be relatively small for when compared with circuit interrupters which operate in air or an insulating gas. This means that the travel distance for closing the contacts is relatively small, which helps to reduce the size of the vacuum bottle.
Typically, a vacuum interrupter comprises a cylindrical high alumina ceramic or similar insulating case having metal end caps or headers which are made of some combination of nickel, iron and/or cobalt. A fixed metal electrode protrudes into the ceramic cylinder and is electrically and mechanically interconnected with one of the end caps. A movable metal electrode protrudes through the other end cap. Contact faces on the ends of the electrodes abut during the circuit making operation for electrical continuity. A relatively flexible, cylindrical, pleated, stainless steel bellows is interposed between and brazed to a portion of the metal movable electrode and its metal end cap so that the entire region inside of the vacuum interrupter may be evacuated. The bellows alternately expands and contracts with the closing and opening respectively of the electrodes to maintain the vacuum integrity of the vacuum chamber it serves to enclose during movement of the movable electrode. The bellows is usually made of relatively thin stainless steel sheet metal (approximately 4 mils). Stainless steel is relatively non-corrosive and has a relatively long life. In addition, the bellows usually occupies space inside the ceramic cylinder. In one case shown in U.S. Pat. No. 4,365,127, entitled "Vacuum Power Interrupter" by Sakuma et al., issued Dec. 21, 1982, an external bellows is shown. Because of the flexibility required, the material which makes up the bellows is relatively thin. But, because the bellows is within the evacuated chamber and close to the contact faces, it is a likely candidate for being exposed to the light, heat and arc by-products of a contact opening operation when an arc is formed and interrupted. This light, heat and by-product of the arc all may cause the bellows to deteriorate, become non-functional or break, thus destroying the vacuum integrity of the switch or interrupter. In the past in order to solve this problem, a fixed metal shield was placed around the bellows between it and the arc region to safeguard it from the aforementioned non-desirable occurrence. An example of a shield can be found in U.S. Pat. No. 4,446,346 entitled "Vacuum Interrupter" issued May 1, 1984 to kashimoto et al. However, both the shield and the bellows take up space within the perimeter of the vacuum chamber and both are electrically conductive. Generally when one is dealing with relatively large vacuum interrupters this is rather insignificant because the volume within the chamber is sufficient to additionally accommodate the shield and bellows. However, it would be desirable to use circuit interrupting or switching devices of a relatively small size when the devices they cooperate with are relatively small. Relatively small motor contactors and similar devices do not utilize vacuum interrupters because no corresponding matching small vacuum interrupter bottles (approximately 1 inch in diameter) are available. The reason that small interrupter bottles are not available lies in the fact that small vacuum bottles have relatively little space within the vacuum chamber for the bellows and the shield. It would be desirous therefore to provide relatively small vacuum interrupter bottles which had either no bellows or no shields in the vacuum chamber.